#include "string.h"
int main()
{
    wang::string s1("hello world");
    wang::string s2(s1);
    wang::string s3("xxxxxxxxxxxx");
    s3 = s1;
    cout << s1.c_str() << endl;
    cout << s2.c_str() << endl;
    cout << s3.c_str() << endl;
    return 0;
}